Method of preparing sodium nitrilotriacetate

ABSTRACT

Preparation of N(CH2COONa)3 in crystalline form by hydrolyzing N(CH2CN)3 in the presence of NaOH. Involves suspending N(CH2CN)3 in recycled mother liquor, adding aqueous NaOH to the suspension, partially hydrolyzing at about 65* to 75*C., further hydrolyzing at about 70* to 90*C. to form N(CH2COONa)3, separating N(CH2COONa)3 from the mother liquor, and recycling the mother liquor.

Umted States Patent 1 1 [1 1 3,715,393 Ribaldone et al. 1 Feb. 6, 1973 i[54] METHOD OF PREPARING SODIUM [56] References Cited NITRILOTRIACETATEUNITED STATES PATENTS [75] Inventors Giuseppe Ribaldwe, Gallamte;3,183,262 5/1965 Singer et a.l. ..26o/534E vatore Gafa, Ferrara, both ofI y 3,463,811 8/1969 Godrey et al. ..260/s34 E [73] Assigneez MomecatiniEdison SJLA Milan, 3,409,666 11/1968 Foremon ..260 534 E Italy PrimaryExaminer-Lorraine A. Weinberger [22] Filed: May 15, 1970 AssistantExaminer-John F. Terapane pp No: 37,817 Attorney--Hubbell, Cohen &Stlefel [57] ABSTRACT [3.0] Foreig Application Priority Data Preparationof 'N(CH COONa) in crystalline form by May 20, 1969 Italy ..1701s A/69 yy g N(CH2CN)3 in the Presence of NaOH- volves suspending N(CH2CN)3 inrecycled mother 52 us. (:1. ..260/534 E liquor, adding aqueous NaOH wthe suspension. P 511 Im. c1..... ..C07c 99/10 tially hydrolyzing atabout to further 581 Field of Search ..260/534 E hydrolyzing at about toto form N(CH COONa) COONa) from the mother liquor, and recycling themother liquor.

3 Claims, 1 Drawing Figure METHOD OF PREPARING SODIUM NITRILOTRIACETATEBACKGROUND OF THE INVENTION 1. Field of the Invention The presentinvention relatesig a process for the preparation of sodium riitrilotriacetate, N(Cl-l COONa) by hydrolysis of nitrilotriacetonitrile,N(CH2CN) with sodium hydroxide.

2. Description of the Prior Art As is well known, sodiumnitrilotriacetate is an important chelating agent, one of its chiefapplications being as an additive for detergents.

Sodium nitrilotriacetate can be prepared by reacting NH with CH O andNaCN in aqueous medium the presence of NaOH. It is thus possible toobtain sodium nitrilotriacetate directly, in the form of an aqueoussolution. The yields, however, are poor and the solution obtainedcontains considerable quantities of byproducts, such as sodiumiminodiacetate, sodium glycolate, and sodium formate, so that it isdifficult to isolate the sodium nitrilotriacetate in the pure form.

Another known method is to effect saponification ofnitrilotriacetonitrile with a substantially stoichiometric amount ofNaOH in an aqueous solution, by gradually adding the nitrile to a warmsolution of NaOH or by mixing the nitrile with NaOH and thereafterheating the mixture to the reaction temperature. However, in such aprocess a solution is obtained, from which the sodium nitrilotriacetatemust be recovered by evaporation, which is a burdensome, time consumingoperation.

SUMMARY OF THE INVENTlON The present invention provides a continuousprocess for hydrolyzing nitrilotriacetonitrile to produce the sodiumsalt of nitrilotriacetic acid, which process results directly in thissalt in crystallized form, along with one mole of water.

In addition to the advantage of directly obtaining a solid product withquantitative yields, the process of this invention offers the advantageof enabling one to operate at relatively low temperatures (6$-90C). Suchlow temperatures are advantageous in that there is less tendency towardcorrosion of the equipment. Moreover, the process of this inventionenables one to obtain a particularly pure and white product.

The present invention provides a continuous process for the preparationof sodium nitrilotriacetate in crystallized form, through the hydrolysisof nitrilotriacetonitrile with sodium hydroxide. The method ischaracterized in that nitrilotriacetonitrile is suspended in recycledmother liquor at a temperature of from about to 60C., and thereafter tothe suspension there is added an aqueous solution of sodium hydroxide inthe stoichiometric quantity necessary to effect hydrolysis of thenitrilotriacetonitrile. The hydrolysis is carried out in two stages, (1)partial hydrolysis at a temperature of from about 65 to 75C., then (2)completion of the hydrolysis at a temperature of from about 70 to 90C.Sodium nitrilotriacetate is then separated from the mother liquor, whichmother liquor is then recycled. The mother liquor that is recycledcontains sodium nitrilotriacetate and sodium hydroxide, the later beingpresent in an amount of from about 20 to percent of the stoichiometricamount with respect to the nitrilotriacetonitrile to be hydrolyzed.

The amount of sodium hydroxide contained in therecycled mother liquor isbetween 20 and 30 percent of the stoichiometric amount required for thehydrolysis of the nitrile. That is, the amount of NaOH present in themother liquor is from about 0.6 to 0.9 mole of NaOH per mole of nitrile.

Description of the Drawing The process of our invention is schematicallytrated in the attached drawing.

Description of the Preferred Embodiments Referring to the drawing, inmixer A there is disposedi via conduit 10 and via conduit 12nitrilotriacetonitrile (NTN) and recycled mother liquor, to thereby forma suspension of NTN in the mother liquor. The temperature of thesuspension is maintained at from about 20 to 60C., as by means of ajacket through which suitable heat transfer fluid may /CH1CONH2 (NwomoooNsh The temperature in reactor R, is maintained at from about toC., as by circulating cold water inside cooling jacket 24 via lines 26and 28, and through evaporation of NH and H 0, which exit via line 30. a

The residence time of the reactants in reactor R, is desirably fromabout 45 to 60 minutes. From about 75 to 90 percent of thenitrilotriacetonitrile is hydrolyzed to sodium nitrilotriacetate (SNTA),while from about 8 to 20 percent of the nitrilotriacetonitrile ishydrolyzed to sodium N(Z-aceto-amide)-iminodiacetate(SADA).

The resulting aqueous suspension of sodium nitrilotriacetate (SNTA),SADA, nitrilotriacetonitrile and NaOH is discharged from reactor R, viaconduit 32 into reactor R in reactor R, the temperature is maintained atfrom about 70 to 90C. by circulation of hot water or stream insidejacket 34 via lines 36 and 38. The residence time of the reactants isdesirably from about 60 to minutes. In reactor R, the residual,unconverted nitrilotriacetonitrile and the intermediate products areconverted into sodium nitrilotriacetate. Gaseous NH, and H 0 exit vialine 39.

The crystals of sodium nitrilotriacetate monohydrate, N(CH COONa) -H,O,together with the mother liquor are passed via conduit 40 to filter F,in which the crystals are separated from the mother liquor. Thefiltering is conducted at a temperature of from about 40 to C. Thesodium nitrilotriacetate crystals are then washed with about 20 percentby weight of water, via conduit 42. This washing water is then added tothe mother liquor. The recovered mother.

liquor, after being cooled down to about 20 to 60C, is then recycled tomixer A via conduit 12.

As previously noted, the mother liquor that is re-cycled contains sodiumnitrilotriacetate (SNTA) as well as NaOH in admixing the recycle motherliquor with nitrilotriacetonitrile (NTN) that is to be hydrolized toillusform a suspension, the admixture is such proportions that the molorratio of SNTA to NTN in the suspension is at least 0.5. A particularlypreferred molar ratio of SNTA to NTN in the suspension is about 0.76.

The sodium nitrilotriacetate crystals, which contain from about topercent by weight of moisture, are

. the third at 80 to 90C. The total residence time of the EXAMPLE l Thisexample was carried out as a continuous process using the apparatusschematically represented in the drawing. In a mixer A there weresuspended continuously every hour 28.6 g of nitrilotriacetonitrile (NTN)in 121.8 g of recycled mother liquor, the temperature of the suspensionbeing maintained at about C. Th

suspension thus obtained contained:

NTN 28.6 g0.2ll mole up 69.8 3370 mole NaOH 7.6 g=0.l89 mole SNTA 44.4g-0J6l mole This suspension was fed at a feed rate of 150.4 g/hr (l2lcc/hr), to reactor R, together with a solution of NaOH (feed rate: 50.6g/hr or 34 cc/hr) consisting of:

NaOH 25.3 5-0633 mole ",0 25.3 g=l .405 mole The reaction mixture wasmaintained at at temperature of about 70C. with a residence time of 60minutes in reactor R, (this reactor having a volume of 155 cc). Theslurry flowing out of reactor R, contained 5.5 percent SADA[N(2-aceto-amide-iminodiacetatel and 92 percent SNTA (sodiumnitrilotriacetate). The slurry was then fed to reactor R, where it wasmaintained at a temperature of about 90C. for 80 minutes in order tocomplete the hydrolysis. The slurry flowing out of reactor R, containedno NTN or SADA.

The amount of NH, and H 0 evolved from R, and R, were as follows:

10.75 [Per hour==0.633 mole per hour l5.2 per how -0.28 mole per hourThe slurry flowing out of R, was then filtered at 90C. and the filtercake of SNTA was washed with l0 g of water. The mother liquor wascombined with the washing water to form the recycle mother liquor whichwas recycled to mixer A.

The color of the recycle mother liquor solution remained constant atfrom 300 to 350 APHA. For each cycle there was an accumulation of CN- ofabout 32 ppm, (resulting from decomposition of thenitrilotriacetonitrile) so that it was necessary to replace a part ofthe recycled liquor about every 100 cycles.

The moist filter cake, consisting of 47.5 g of SNTA and 5. g of H O, wasdried in an oven. The dry product was essentially free of SADA andshowed a content of SNTA in excess of 98 percent. About 80 percent ofthe product was in the form of granules of from 0.1 to 0.25 mm.

EXAMPLE 2 A continuous example was carried out using the same reactantsand under the same conditions as described in example 1. Three reactorswere employed, the first and second each being maintained at C., and thethird at 90C. Theresidence time for the mixture in each reactor was 30minutes. Aqueous NaOH solution was fed only into the first reactor.

The mixture exiting from the second reactor contained 1.5 percent SADAand 98.5 percent SNTA. The product exiting from the third reactor wasfree of SADA. The content, expressed as sodium nitrilotriacetatemonohydrate, of the dry product was in excess of 98 percent. The amountsof the products involved in the reaction and the color of the solutionwere the same as in example i. In this example, as in example 1, therewas an increase of CN- in solution equal to about 32 ppm per each cycle.The CN- originated from the decomposition of the nitrilotriacetonitrile.

Modifications and variations can, of course, be made with departing fromthe spirit and scope of the invention.

Having thus described our invention, what wedesire to secure by LettersPatent and hereby claim is:

' l. in a continuous method of making sodium nitrilotriacetate incrystalline form by hydrolyzing nitrilotriacetonitrile in the presenceof sodium hydroxide, the improvement comprising a. suspendingnitrilotriacetonitrile in recycled mother liquor, said mother liquorcontaining sodium nitrilotriacetate and sodium hydroxide, the amount ofsodium hydroxide contained in said mother liquor being from about 20 to30 percent" of the stoichiometric amount required to effecthydrolysis'of said nitrilotriacetonitrile, the temperature of saidsuspension being maintained at from about 20 to 60C,

b. adding to said suspension an aqueous solution of sodium hydroxide inan amount of 3 moles of NaOH per mole of nitrilotriacetonitrile wherebythe total amount of NaOH in the reaction mixture is about 3.6 to 3.9moles per mole of nitrilotriacetonitrile,

. partially hydrolyzing said nitrilotriacetonitrile at a temperature offrom about 65 to C to form a mixture comprising sodium nitrilotriacetateand sodium-N-(Z-acetamido)-iminodiacetate,

. completing the hydrolysis at a temperature which is higher than thetemperature in step (c) and which is from about 70 to C to form sodiumnitrilotriacetate, separating and recovering sodium nitrilotriacetatecrystals from said mother liquor, and

water is then recycled.

3. The method of claim 1 wherein said sodium nitrilotriacetate isseparated from the mother liquor at a temperature of from about 40 to C.

Po-ww usurp STATES rirrnr ClFlElClE 9) V m mm a 1 ChllllrlCAlh ClCtlllllntliCN Patent No" 3,715, 393 Dated February 6, 1973 InvmmorhflGIUSEPPE RIBALDONE and SALVATORE GAFA It is certified that error appearsin the ahove identified patent and that said Letters Patent are herebycorrected as shown below:

Abstract, line l: Preparation of should read A method of preparingAbstract line 2e3; "NaOH. Involves" should read NaOH which comprisess -aAbstract line 7: "N(CH COONa) COONa) from" should read N(CH COONa)separating NfCH CflONa) from w Column l line 6: process should read memethod r0 Column l line 8: hydrolysis of" should read hydrolyzing Columnl, line 15: medium the" should read medium in the Column 1, lines l8-l92"solution obtained should read we obtained solution Column 1, line 22:in the pure" should read in pure Column 1, line 29: process should readmethod Column 1, line 34: process should read method Column 1 line 36:,"process should read method Column l line 37: directly in this shouldread directly in the production of this Column l lines 40-41: "the'process of this should read the method of the Column 1, line 46: processof this" should read method of the "-0 Column l, line 48: process shouldread method Column l lines 54 55: thereafter to the suspension there isadded" should read thereafter, there is added to the suspension -uColumn 2 line 8: "the process of our should read the method of the oColumn 2, line l7: which suitable should read which a suitable Column 2,line 45: stream should read steam -a Column 2 line 62: -"cooled down to"should read cooled to Column'3, lines 9-10: the method of thisinvention, the proc should read the invention, the method Column 3, line11 "process should read method Column 3 line 19:

L mi

UMTED s'rjmzs PAT}??? OFFEZCE (ZERTEFEQATE @F CQRREQJTIGN Patent No. 3J715, 393 Dated February 6,

Inventoz-(s) GIUSEPPE RIBALDQNE and SALVATORE GAFA It is certified thaterror appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

"process" should read method Column 3, line 29: "as a continuousprocess" should read continuously Column 3, lines 36-39: NTN NTN gggshould read :ggg SNTA SNIA Column 3, lines 46-47:

" NaOH -Na0H 2 should read Column 3, line 47: "mole" should read molesColumn 4-, line 3: "CN should read CN' Column 4, line 6: "part" shouldread portion Column 4, line 30: "CN should read CN Column 4, line 31:"CN should read CN" Column 4, line 35: "with" should read without Signedand sealed this 25th day of December 1973.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. RENE D. TEGTMEYER Attesting Officer ActingCommissioner of Patents

1. In a continuous method of making sodium nitrilotriacetate incrystalline form by hydrolyzing nitrilotriacetonitrile in the presenceof sodium hydroxide, the improvement comprising a. suspendingnitrilotriacetonitrile in recycled mother liquor, said mother liquorcontaining sodium nitrilotriacetate and sodium hydroxide, the amount ofsodium hydroxide contained in said mother liquor being from about 20 to30 percent of the stoichiometric amount required to effect hydrolysis ofsaid nitrilotriacetonitrile, the temperature of said suspension beingmaintained at from about 20* to 60*C, b. adding to said suspension anaqueous solution of sodium hydroxide in an amount of 3 moles of NaOH permole of nitrilotriacetonitrile whereby the total amount of NaOH in thereaction mixture is about 3.6 to 3.9 moles per mole ofnitrilotriacetonitrile, c. partially hydrolyzing saidnitrilotriacetonitrile at a temperature of from about 65* to 75*C toform a mixture comprising sodium nitrilotriacetate andsodium-N-(2-acetamido)-iminodiacetate, d. completing the hydrolysis at atemperature which is higher than the temperature in step (c) and whichis from about 70* to 90*C to form sodium nitrilotriacetate, e.separating and recovering sodium nitrilotriacetate crystals from saidmother liquor, and f. thereafter recycling said mother liquor.
 2. Themethod of claim 1, wherein said crystals of sodium nitrilotriacetateseparated from the mother liquor are washed with water, the wash wateris then added to the mother liquor, and the mother liquor-water is thenrecycled.